1. Field of the Invention
This invention is in the field of cutting apparatus and more particularly relates to apparatus for cutting segments of layers of dry film photoresist overlaying tooling holes of printed wire circuit blanks and for removing these segments.
2. Description of the Prior Art
In electronic systems, particularly those which are relatively complex, there is a need for compact arrangements of components of such circuits. The components are frequently mounted on printed wire boards (PWB)s and interconnected by conductors produced on such (PWB)s by photolithographic processes. Such processes start with a PWB blank, a thin laminate, or base, of epoxy glass, for example, with its upper and lower surfaces covered with a thin layer of copper. The PWB blanks are provided with a number of tooling holes, three to five, for example, which are used to precisely position the blanks in order that the individual conductors when produced will be precisely positioned.
After the tooling holes have been drilled in a PWB blank, and any other holes that are to be formed in the blank have been drilled and plated with copper, the next step in the process of producing finished PWBs is to apply layers of dry film photoresist over the copper layers of PWB blanks. The two layers of photoresist are then laminated to the blank by the application of pressure and heat. The dry film photoresist has a coating of adhesive material which secures the layers of dry film photoresist to a PWB blank.
In the process of applying the layers of photoresist to a PWB blank, the tooling holes of the blank are covered. To convert a PWB blank into a finished PWB, it is necessary to expose the photoresist to a source of radiant energy, to develop the exposed photoresist film, to etch the copper that is to be removed to produce conductors, and to strip away the remains of the photoresist on the PWB. However, to properly expose the photoresist so that the conductors will be formed where intended with the proper degree of precision, it is necessary that the tooling holes be accessible so that they can be used to properly position the PWB blank.
The prior art way of removing layers of dry film photoresist overlaying, or covering, tooling holes of the PWB blank has been by individual operators using a knife to cut the layers. The segments of the photoresist layers are then removed by hand.
There are two problems with the prior art manner of removing layers of dry film photoresist overlaying tooling holes, one is that it takes a substantial amount of time to perform this operation with acceptable precision. In addition, the heat and the pressure applied to laminate photoresist layers to a PWB blank causes the photoresist to become brittle. Thus, in cutting the layers of photoresist overlaying a tooling hole, flakes or particles of the photoresist are frequently produced. If these particles are not detected and removed they will cause shorts to be produced between separate conductors formed on a finished PWB. The necessity for removing these particles increases the cost of removing photoresist overlaying tooling holes, and to the extent such particles are not completely removed, additional work is required to correct the resulting shorts which further increases the cost of the operation.